As the information age progresses, display devices visually displaying a large amount of data on the basis of an electric signal are being rapidly developed. As a result, flat panel display devices with superior features such as light weight, slimness, and low electric power consumption have been widely distributed. Flat panel display devices include liquid crystal display (LCD) devices, plasma display panel (PDP) devices, field emission display (FED) devices, organic electro luminescence display (OELD) devices, and so on. A cathode ray tubes of related art are rapidly being replaced with flat display devices. Many researches are being waged to improve the display quality of the flat display devices. Particularly, the LCD has gradually improved from disadvantages of high power consumption and viewing angle area that have been raised as drawbacks of LCD.
Unlike other display devices such as a Cathode Ray Tube (CRT), and a Plasma Display Panel (PDP), a liquid crystal display panel used in an LCD cannot generate light by itself. Therefore, an LCD requires a separate light source which can provide the liquid display panel with light and a backlight unit including the light source. That is, since the liquid crystal layer is not self-emissive, the LCD module also has a backlight assembly, which is located behind the TFT panel, to provide light to the liquid crystal layer.
The backlight assembly includes a mold frame formed with an accommodating space, a reflective sheet disposed at a base surface of the accommodating space to reflect light toward liquid display panels, a light guide plate formed at an upper surface of the reflective sheet to guide the light, a lamp unit formed between the light guide plate and a lateral surface of the accommodating space to emit the light, an optical sheets stacked on the upper surface of the light guide plate to diffuse and collect the light, and a top chassis formed at an upper surface of the mold frame to cover an area from a predetermined corner position of the liquid crystal panel to a lateral surface of the mold frame.
The optical sheet includes diffusion sheets for diffusing light, prism sheets stacked on an upper surface of the diffusing sheet to collect the diffused light and to transmit the collected light to the liquid crystal panels, and a protective sheet configured to protect the diffusing sheets and the prism sheets.
Particularly, configuration of optical sheets is highlighted for implementing improvement of luminance, low power consumption and slimness which are the trends of current LCD televisions. To this end, the reduced number of lamps and backlight unit of LED have been introduced, and effect of diffusing function and luminance improvement is greatly required from the optical sheets of the backlight unit.
Currently, the technique to simultaneously satisfy the improvement of luminance and diffusing function is a method of irregularly distributing lens-shaped patterns on the optical sheets. FIG. 1 is a plan view illustrating an optical sheet formed with irregular patterns according to prior art.
Referring to FIG. 1, lens-shaped patterns irregularly formed on ultraviolet resin are seen. The irregular pattern arrangement still suffers from dissatisfaction resulting from such characteristics as low power consumption, poor luminance and poor diffusion of LCD despite recent development of improved luminance and diffusion function. The reason is that it is difficult to control the optical characteristic because the arrangement is irregular based on the pattern sizes. To be more specific, it is difficult to control the packing factor and sag (lens height/lens diameter) of lens, which are the most important factors for determining the characteristics of luminance and diffusibility.
Therefore, it is necessary to require an arrangement of regular patterns for improving the characteristics of luminance and diffusion. However, the use of regular patterns may cause an occurrence of a Moire pattern beating due to repeated periodicity with LCD panels. Moreover, the Moire pattern beating may cause reduction of luminance and unbalanced screen image, which may act as a limitation to application of regular patterns.
As a result, optical sheets having regular patterns are required in earnest in order to control the packing factor and sag of lens, and to prevent the Moire pattern beating as well.
And, light bulbs such as fluorescent lamp, incancescent lamp was used as a light source at home. So quality of light is not good and dazzling is brought about because the light bulbs are driven by commonly used alternating current frequency, which cause user's eye to be tired. To reduce the aforementioned disadvantage, optical sheet which can improve a luminance of light bulbs and reduce the eye-tiredness and prevent a amblyopia by being positioned at the light outlet, is required.